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G8MNY > TECH 13.10.25 16:06l 156 Lines 6968 Bytes #10 (0) @ WW
BID : 42716_GB7CIP
Subj: 2M 65W PA with 2x M6774H
Path: JH4XSY<N3HYM<VE3CGR<CX2SA<ED1ZAC<GB7CIP
Sent: 251013/0654Z @:GB7CIP.#32.GBR.EURO #:42716 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Mar 23)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
My local club had a source of these Class C VHF PA blocks. The specification
for them is a max of 500mW drive for 33W out on 12.5V, but the H type is
150-175MHz! So there usefulness on 2m was unknown, although some 2m kit was
reported to use them.
ﾚﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄｿ
Heatsink ｳ ｳ ｳ ｳ I tested one on a heatsink with just coax
is groundｳoｳ M 6 7 7 4 H ｳoｳ connected & it produced 33W, so all looked good.
ｳ ｳ ｳ ｳ
ﾀﾄﾁﾂﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾁﾄﾙ DC1 powers the 1st low current stage,
ｳ ｳ ｳ ｳ DC2 @ 8A Max for full output.
in DC1 DC2 out
A 1.5W handheld can do more drive than that, so I used 2 of them to make a 2m
PA with a good power level out of junk bits.
ﾚﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄｿ
A PCB (double sided) was cut ﾞﾛﾝ ﾞﾛﾝ
to fit over the heat plate & ﾞﾟﾝ M 6 7 7 4 H ﾞﾟﾝ
under the screws & connection ﾞﾛﾝ ﾞﾛﾝ
wires, to provide connection ﾞﾛﾝﾂﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾞﾛﾝ
pads, through links were put ﾞﾛﾝﾛ ﾛﾞﾛﾛﾛﾝﾛﾞﾛﾝﾛﾞﾛﾝ
in to. An old 900MHz phone PA ﾞﾛﾝﾟ ﾟﾞﾛﾛﾛﾝﾟﾞﾛﾝﾟﾞﾛﾝ
casting was used as heatsink ﾞﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾛﾝ
& case.
2 PA MATCHING PRINCIPLE
Assuming the PA blocks are identical in power level, gains, & signal phases
(time delay). Then there are a couple of ways to connect them, I have used the
simplest using just coax.
To match the 2 PA blocks to the 50ohm input & output, 4x 1/4 wave 75ohm coaxes
are needed to make the connections. Each 75ohm 1/4 wave transforms the 50ohm to
approx 100ohm & 2 of these paralleled up give 50ohm again.
50Rﾚﾄﾄﾄﾄﾄｿ50R
ﾉﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｵBLOCKﾆﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｻ
ｺ ｬ Wave 75R ﾀﾄﾄﾄﾄﾄﾙ ｬ Wave 75R ｺ
50R Inﾄｶ ﾇﾄ50R Out
ｺ ｬ Wave 75R ﾚﾄﾄﾄﾄﾄｿ ｬ Wave 75R ｺ
ﾈﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｵBLOCKﾆﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｼ
50Rﾀﾄﾄﾄﾄﾄﾙ50R
I measured the velocity factor of a good length of the 75ohm coax (0.6 - 0.90
the speed of light depending on the type of coax) with an open circuit teed on
a signal generator & scope/(Detector) & adjusted the frequency to give a null
which was 22MHz for my length. This meant I needed 22/145 times this length to
get the same @ 2m (46cm for my white foam filled coax).
PA SCHEMATIC
ﾚﾄﾄﾄﾄﾄﾄｿ
ｳRF PTTﾃﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳ Senseｳ ｳ ﾚﾄﾄﾄﾄﾄｿ ｳ
ﾀﾄﾄﾄﾄﾄﾂﾙﾚﾄﾄﾁﾄﾄｿ ﾉﾍﾍﾍﾍﾍｵBLOCKﾆﾍﾍﾍﾍﾍｻ ﾚﾄﾄﾁﾄﾄﾄｿ
RIGﾍﾍﾍﾍﾍﾍﾍﾍﾏﾍｵDRIVEｳ ｺ 75R ﾀﾄﾄﾄﾄﾄﾙ 75R ｺ ｳOUTPUTﾃ(o AERIAL
50ohm ｳRELAYﾃﾄｶ ﾇﾄｴRELAY ｳ SO239
Coax ﾀﾄﾄﾒﾄﾄﾙ ｺ 75R ﾚﾄﾄﾄﾄﾄｿ 75R ｺ ﾀﾄﾄﾒﾄﾄﾄﾙ
ｺ ﾈﾍﾍﾍﾍﾍｵBLOCKﾆﾍﾍﾍﾍﾍｼ ｺ
ｺ ﾀﾄﾄﾄﾄﾄﾙ ｺ
ﾈﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍｼ
50ohm Rx coax
CIRCUITS ﾚﾄﾄﾄﾄ>To Handheld Rig
2x 1N4148 ﾚﾄ100Rﾄｿ ｳ
ﾚﾄｴ>ﾃﾄﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄｴ<ﾃﾄﾁﾄﾄﾄﾄﾂﾄﾄﾄﾄo\oﾄﾄﾄﾁﾂﾄﾄo-oﾄﾄ< +12V
ｳ === ｳ/e ===30n //TX 1K ON ｳ 13A Car lighter
* ﾃﾄｴ<ﾃﾄﾄﾁﾄﾄﾄｴPNP _ｳ_ LED _ｳ_ ｳ ﾚﾄ< 0V
4pFｳ 1n ｳ\ \_/=ON 12V _ｳ_
=== ﾃﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄ470Rﾂﾄﾄﾄﾄﾄｿ ｳ LED to PA
1W>ﾄﾄﾁ>Drive ﾚﾄﾄﾄﾁﾄﾄｿ ｳu1ｳ ｳ ﾚﾄﾄﾁﾄﾄｿ _ｳ_ Blocks
Rig Relay ｳOutputｳ === ｳ +ｳ ｳDriveｳ
Common ｳRelay ｳ ｳ _ｳ_ === ｳRelayｳ5V
ﾀﾄﾄﾄﾂﾄﾄﾙ12Vｳ /_\ 10uｳ ﾀﾄﾄﾂﾄﾄﾙ
ﾃﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾙ
_ｳ_ 1N4148
A tiny amount of drive RF current is fed through the 4pF to voltage doubler to
turn on the PNP (* I tried different values, & this worked with my PNP & relay
load @ 100mW low drive power). The 2 changeover relays are both plastic
encapsulated ones, the drive one is a smaller 5V DIL type, they are both held
in place with a local earth tag soldered to the coil connection & the coaxes
ground there too.
The RF detector & relay drive PNP transistor are mounted UGLY fashion around
the drive relay.
To stop the output relay operating when RF power is present, I delayed the
driver relay by about 1/100 second, with the 470 & 10uF. I checked the drive
relay operated on low RF power 100mW & low voltage of 11V OK, even with the
series Tx LED!
The diode across the relays stop back EMF from damaging the PNP, the u1 cap
across the output relay coil reduced VHF RF pickup on the wiring when 65W is on
the contacts!
For each PA block
ﾚﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄｿ
ｳ ｳ ｳ ｳ Power filtering capacitors are
ｳoｳ M 6 7 7 4 H ｳoｳ applied to each module keeping the
ｳ ｳ ｳ ｳ leads short for good VHF practice.
ﾀﾄﾁﾂﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾁﾄﾙ75ohm Coax A ferrite bead (FB) is used to feed DC1.
ﾙ ｳ _FB ｳ ﾀ
_ｳ_ ﾃﾄﾄﾄﾂﾄﾄﾄﾂﾄﾁﾄｿ _ｳ_ The 1N4001 is only there in case
ｳ ~ ｳ _ｳ_ +ﾃﾄﾄﾄﾄﾄﾄﾄ+12V of power rail reversal & 2 of them
u1=== === /_\ === should be able to blow the 13A fuse.
ｳ6n8ｳ ｳ ｳ1000uF
ﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁｿ
1N4001 _ｳ_
LAYOUT
Fitting in all the coax ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
is the main problem with ｳ [ｱｱｱｱｱ] ﾃｿSO
this design, as my finned ｳ ｳ_____ｳ[]ﾃﾙ239
blackened dye cast box was ｳ PNP O/Pﾃ Tx LED
is only 18 x 13 x 3cm. ｳ[] =]Fuse
ｳDrive ﾃ On LED
Heat conductive paste is ｳ [ｱｱｱｱｱ] ﾘﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍﾍ12V Lead
put under the modules & ｳ ｳ_____ｳ ] On Sw
the temperature remains ｳ ﾘﾍﾍﾍﾍﾍﾍﾍﾍﾍto Rig
quite cool for short overs. ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
(Fan might be needed for heavy use)
RESULT
With 13.8V & just over 1W drive output was a good 68W, 13A drawn & with 200mW
about 50W needing only 10A.
Harmonics from these modules are quite low, I measured them at >-30dBc (near
the limit of my testgear @ VHF), but I did add a RF pi low pass filter @ the
aerial socket.
Tx relayﾄﾄﾄﾄﾄﾂﾄ()))ﾄﾂﾄﾄﾄﾄo)SO239 The 23pF caps are 2 Tx grade ceramic
ｳ23pF=== L ===23pFｳ the L is 2 turns, dia & wire gauge
ﾁﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾙ select for 1:1 SWR match on test.
If the modules are misterminated of course anything can happen & as with many
PAs loads of sprogies might result!
Through/Rx loss was 0.5dB with 1m of driver coax & BNC in circuit. A switched
Mutek well filtered preamp was fitted in the Rx path, so the PA not powered up
the drive power was available, this overcomes any Rx insensivity as well as
proving good out of band Rx protection.
See my tech buls. "RF Modules List", "Scope RF Trick", "Coax Traps", "Non relay
instant RF Switching", "DC/RF Sensing PA Switching", & "2m Cavity Filter".
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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